In recent years, image forming devices such as Multi Function Peripherals (MFP) have been used to generate graphics on sheet-shaped media such as paper (hereinafter collectively referred to as “the paper”). In addition, erasable coloring materials such as ink containing leuco dye have been used to print graphics on the paper in order to erase graphics on the papers for the purpose of recycling. Applying a higher temperature erases the color. An color erasing apparatus, including a platen roller facing a heat source and a conveying path of the paper in the middle, heats the paper by conveying the paper in between the platen roller and the heat source, and erases the erasable coloring material.
However, the conventional color erasing apparatus conducts heating at a certain condition regardless of the thickness of the paper. Therefore, the output power for the heat source for erasing a color is controlled is the same for thicker papers having a higher heat capacity as it is for papers having a lower heat capacity. Consequently, there is a problem of higher power consumption.